1. Field of the Invention
The present invention relates to a liquid ejection head, a method of manufacturing same, and an image forming apparatus, and more particularly to a liquid ejection head, a method of manufacturing same and an image forming apparatus, in which connections for drive wires which supply drive signals to piezoelectric elements are devised, in a liquid ejection head using the piezoelectric elements as pressure generating devices for ejecting liquid.
2. Description of the Related Art
As an image forming apparatus, an inkjet printer (inkjet recording apparatus) is known, which comprises an inkjet head (liquid ejection head) having an arrangement of a plurality of nozzles (ejection ports) for ejecting ink (liquid) and which forms images on a recording medium by ejecting ink from the nozzles toward the recording medium, while causing the inkjet head and the recording medium to move relatively to each other.
For example, as an ink ejection method for an inkjet recording apparatus of this kind, a piezoelectric method is known, in which a diaphragm which constitutes one face of a pressure chamber is deformed by the deformation of a piezoelectric element by using the piezoelectric element as a pressure generating device for ejecting ink, thereby changing the volume of the pressure chamber, ink is introduced into the pressure chamber from an ink supply passage when the volume of the pressure chamber is increased, and the ink inside the pressure chamber is ejected from a nozzle in the form of an ink droplet when the volume of the pressure chamber is decreased.
Furthermore, in recent years, it has been sought to form high-quality images similar to photographic prints, with inkjet recording apparatuses of this kind, and for this purpose, it has been necessary further to reduce the size of the ink droplets ejected from the nozzles by reducing the size of the nozzles, as well as arranging a plurality of nozzles at higher density.
This in turn requires the pressure chambers which are connected to the nozzles to be disposed in a high-density arrangement, in conjunction with the increased density of the nozzles. Furthermore, the electrical wires (drive wires) which supply drive signals to the piezoelectric elements disposed corresponding to the pressure chambers must also be arranged at higher density. Various proposals have been made in order to achieve higher density arrangement of the nozzles in this manner.
For example, Japanese Patent Application Publication No. 2001-113700 discloses an inkjet head in which, in order to provide an inkjet head which readily achieves a large number of nozzles and high density arrangement of the nozzles, it is sought to reduce the size of the head by electrically connecting energy generating devices (piezoelectric elements) on a head substrate with connection devices (drive wires), via through holes provided in the head substrate.
As described above, in order to achieve high recording speed and high image quality in an inkjet recording apparatus, it is essential to increase the number of nozzles and to arrange the nozzles at higher density, and consequently, the number of wires providing the electrical connections to the piezoelectric elements corresponding to the nozzles increase in number. It is difficult to increase the density of the wiring, by means of a one-dimensional or a two-dimensional wiring arrangement in which the wires are extended in a horizontal direction, and hence it is necessary to adopt a three-dimensional wiring arrangement using through holes, for example.
Furthermore, as described above, in an inkjet recording head based on a piezoelectric method, a portion of each of the pressure chambers connected to the nozzle openings which eject ink droplets is constituted by a diaphragm, and by causing this diaphragm to deform by means of a piezoelectric element, the ink in the pressure chamber is pressurized, and an ink droplet is ejected from the corresponding nozzle opening. There are two types of piezoelectric elements, namely, the vertical vibration mode (d33 mode), in which the piezoelectric element deforms in the same direction as the direction of the electric field, and expands and contracts in the axial direction, and the bending vibration mode (d31 mode), in which the piezoelectric element deforms in a direction perpendicular to the direction of the electric field, and the piezoelectric element bends.
In the case of a system which uses a piezoelectric element operating in the vertical vibration mode, it is possible to increase the amount of displacement of the piezoelectric element in the direction toward the diaphragm, by holding the piezoelectric element from the opposite side to the diaphragm, with a fixed plate. Therefore, it is possible to make the upper part of the piezoelectric element adhere closely to the fixed plate. Consequently, it is possible to form piezoelectric elements previously on the surface of the fixed plate, and to form wires in a through hole shape in the fixed plate, in order to connect to the electrodes of the piezoelectric elements.
On the other hand, when using piezoelectric elements operating in the bending vibration mode, if the piezoelectric elements adhere tightly to the fixed plate, then it is not possible for the piezoelectric elements to bend, and therefore, a space which allows the piezoelectric elements to bend must be ensured on the opposite side of the piezoelectric elements from the diaphragm (namely, a space which prevents obstruction of the movement of the piezoelectric elements). Moreover, in order to protect the piezoelectric elements, this space must be a hermetically sealed space which covers the upper portion of each piezoelectric element. Therefore, when using piezoelectric elements operating in the bending vibration mode, connections with the through holes on the upper side must be made within this hermetically sealed space.
However, in the head described in Japanese Patent Application Publication No. 2001-113700, the electrical connections to the piezoelectric elements are made via through holes provided in the head substrate directly below the piezoelectric elements, but no consideration is given to providing spaces for preventing obstruction of the movement of the piezoelectric elements, as required when piezoelectric elements operating in the bending vibration mode are used as described above. If piezoelectric elements operating in the bending vibration mode are used, then a problem arises when it is sought to make the electrical connections via these through holes.
For example, when the electrodes of the piezoelectric elements are connected to the wires via through holes, then if a semi-fluid material, such as solder, conductive paste, or the like, is used, the semi-fluid material may be project beyond the region where it is originally required, inside the hermetically sealed space, and hence there is a risk that this projecting material may obstruct the movement of the piezoelectric elements. Furthermore, since the electrical connections are made within a hermetically sealed space, it is not possible to confirm the connection status, and there is a risk of connection defects.